Locomotor recovery in spinal cord-injured rats treated with an antibody neutralizing the myelin-associated neurite growth inhibitor Nogo-A - PubMed (original) (raw)

Locomotor recovery in spinal cord-injured rats treated with an antibody neutralizing the myelin-associated neurite growth inhibitor Nogo-A

D Merkler et al. J Neurosci. 2001.

Abstract

The limited plastic and regenerative capabilities of axons in the adult mammalian CNS can be enhanced by the application of a monoclonal antibody (mAb), IN-1, raised against the myelin-associated neurite growth inhibitor Nogo-A. The aim of the present study was to investigate the effects of this treatment on the functional recovery of adult rats with a dorsal over-hemisection of the spinal cord. Directly after injury, half of the animals were implanted with mAb IN-1-secreting hybridoma cells, whereas the others received cells secreting a control antibody (anti-HRP). A broad spectrum of locomotor tests (open field locomotor) score, grid walk, misstep withdrawal response, narrow-beam crossing) was used to characterize locomotor recovery during the 5 weeks after the injury. In all behavioral tests, the recovery in the mAb IN-1-treated group was significantly augmented compared with the control antibody-treated rats. EMG recordings of flexor and extensor muscles during treadmill walking confirmed the improvement of the locomotor pattern in the mAb IN-1-treated rats; step-cycle duration, rhythmicity, and coupling of the hindlimbs were significantly improved. No differences between the two groups with regard to nociception were observed in the tail flick test 5 weeks after the operation. These results indicating improved functional recovery suggest that the increased plastic and regenerative capabilities of the CNS after Nogo-A neutralization result in a functionally meaningful rewiring of the motor systems.

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Figures

Fig. 1.

Fig. 1.

Evaluation of lesion size at the epicenter of the injury at thoracic level Th8. SWM was assessed from alternating sagittal sections of the spinal cord (arrows) and set in relation to the amount of white matter in the intact spinal cord rostral to the lesion (equaling 100%). Sections at the center of the spinal cord are shown from a control animal and an IN-1 Ab-treated animal.

Fig. 2.

Fig. 2.

Recovery monitored with the BBB open-field locomotor score. A, Time course of the recovery in IN-1-treated and control Ab-treated rats (n = 17 rats per group). B, Comparison of single animals with regard to BBB score 35 d after injury. Note the two subgroups in the mAb IN-1-treated animals. C, Correlation between SWM and the BBB locomotor score of single animals and the regression lines of the two groups. Data are given as means ± SEM; *p < 0.05.

Fig. 3.

Fig. 3.

Grid walk performance. A, Time course of the recovery in IN-1-treated and control Ab-treated rats (n = 17 rats per group) shows significantly lower error rates in the mAb IN-1 animals. B, Latency of the onset of the withdrawal movement in the case of a stepping error on the grid. The stick figure is illustrating the measurement (also see Materials and Methods). C, Bar graph (means ± SEM) showing that mAb IN-1-treated rats have recovered their response latency to preoperative values, in contrast to the control animals. *p < 0.05; **p < 0.01.

Fig. 4.

Fig. 4.

Time course of the recovery in IN-1-treated and control Ab-treated rats in the narrow-beam test (_n_= 17 rats per group). The ability of the rats to walk on differently shaped wooden beams is scored from 0 to 6 (see Materials and Methods). Data are given as means ± SEM; *p < 0.05; **p < 0.01.

Fig. 5.

Fig. 5.

EMG recordings of treadmill-walking rats 40 d after lesion from two hindlimb muscles in rats with different locomotor scores. A, Only the recorded flexor muscle TA was found to be rhythmically active. In comparison with an uninjured rat (D), the contractions were prolonged and irregular, and the frequency was fairly low. The extensor muscle VL rarely shows activity. B, The extensor muscle VL is more active and bursts in a more rhythmic pattern. Cocontractions between the muscles occurred frequently. C, The flexor (TA) rhythm is increased, and the bursts are more defined and shorter. In addition, the extensor (VL) bursts are more regular and are well coordinated with the flexor muscle. D, Recordings of an intact control animal.

Fig. 6.

Fig. 6.

Evaluation of EMG recordings 40 d after injury: step-cycle duration and rhythmicity. A, The correlation between the BBB locomotor score and the step-cycle duration of all EMG implanted rats 40 d after lesion showed a decrease in the duration with increasing performance in the open field.B, A correlation between the deviation in the step-cycle duration and the BBB locomotor score 40 d after lesion indicates a strong relationship between an increase in open field performance and a more regular stepping pattern. C, A comparison of the average step-cycle duration (means ± SEM) as well as its variation (shown as SD) between IN-1-treated and control Ab-treated rats shows a highly significant improvement in the mAb IN-1 group. **p < 0.01.

Fig. 7.

Fig. 7.

A, Cocontractions between the VL and the TA occurred frequently in all spinal cord-injured rats especially at BBB scores of <12. Because some animals did not show patterned extensor activity, no statistical comparison was performed. The black bars and white bars represent the activity pattern of the TA and the VL muscles, respectively.B, Uncoupling of the rhythmically active hindlimbs (arrows) occurred in animals of both treatment groups, especially in rats with a BBB score of <10. An example for the right and left TA is shown.

Fig. 8.

Fig. 8.

No significant changes were observed in the withdrawal response to a nociceptive stimulus (infrared beam) at 35 d after injury in the tail flick test (means ± SEM;n = 17 rats per group).

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